N EW YORK — Winston Churchill ranks among the greatest 20th century politicians and leaders in the world.

But Brian Cox, who portrays him in the up-close and personal “Churchill,” which opened Friday, grew up in Dundee, Scotland, thinking he was a traitor.

“My relationship,” said Cox, 70, “has nothing to do with any previous portrayal of Churchill, but my relations. When I was a kid, Churchill would come on the radio — and people didn’t trust him because he’d changed parties. He was not popular.”

“Churchill” presents England’s wartime prime minister in June 1944 as the Allied generals plan D-Day, the final push to defeat Germany and retake Europe. (Boston native John Slattery, best known from “Mad Men,” co-stars as Dwight Eisenhower.) Churchill loudly opposes the invasion of Normandy’s beaches.

Churchill, the actor said, isn’t exhibiting early signs of dementia though, “He was clearly ill. He had pneumonia at the end of ’43 and was a man who drank this phenomenal amount of alcohol. The fact that he lived to be 90” — he died in 1965 — “was unbelievable!

“To play Churchill, you have to get inside the man, because there were so many Churchills,” Cox continued.

“There is this brilliant star, a scholar, Shakespearean in his eloquence and rhetoric, a master of the microphone. That was his personality.

“There was a private Churchill. But the ‘little boy Churchill’ with the cigar-smoking? That’s like thumb sucking. I understood his isolation in his early years in his childhood. He was a lonely little fat boy. His father was syphilitic. His mother was a snob, very ambitious. He wasn’t loved in the same way so he had, in a way, to take care of himself.”

“I have the same problem,” Cox revealed. “My father died when I was 8, and I find being a father the most difficult thing in the world. I have four (children).

“My mother had a nervous breakdown — she wasn’t present. So I understand that lonely desperation. I was more or less left to my own devices, and that’s how I got into this business. I spent all my time in the cinema. It was me and my imagination.

“My kids complain to this day, and I go, ‘Tough! I ain’t Mr. Perfect.’ I can totally empathize with Churchill.”

Film critic and entertainment reporter Stephen Schaefer writes regularly for The Boston Herald with interviews, features, reviews and "Hollywood & Mine," a weekly BostonHerald.com/entertainment/movies column. He frequently speaks with film clubs about upcoming releases and often covers film festivals in Berlin, Venice, New York and Toronto.